In German patent application DE 1 421 451 (A B Dick Company), a lithographic offset master is described comprising a base sheet having an ink repellant, water receptive, lithographic surface having a continuous coating of a dispersed phase of an ink receptive, water repellant imaging material uniformly distributed in a binder system. The coating is capable of displacement from the surface of the base sheet by solution or dispersion in water and/or alcohol. The printing plate is developed, for example, by wiping the plate with an etching composition.
Japanese patent application JP 63100460 (Konica Corp.), shows a method and apparatus for processing photosensitive material with improved stability or the like. Different developing liquids are used in two developing stations.
French patent application FR 2 402 231 (Beach manufacturing Corporation) describes a method and apparatus for automatically producing finished lithographic plates from supplies of blank plates and negatives. The plates are developed in a completely enclosed apparatus using a number of different liquids.
European patent application EP 0 260 615A (Hoechst AG), describes a compact device which can be attached to a conventional printing plate developing machine either as a correcting agent washing station or as a developing station. The developing machine has separate developing, rinsing and gumming stations.
European patent application EP 0 177 890A (Hoechst AG) describes a device for treating printing plates with a fluid. A single cell apparatus is shown for developing negative or positive printing plates of undisclosed form.
Methods of making lithographic printing plates are known, for example from European patent applications EP 0 769 724-A and EP 0 768 172-A (Agfa-Gevaert NV), which comprise the steps of:
(1) image-wise exposing to radiation an imaging element comprising on a plastic film support at least one radiation sensitive layer composition, the composition being such that when exposed and developed, a lithographic surface is formed; and PA1 (2) developing the thus obtained image-wise exposed imaging element on a printing press using a single developing fluid, for example with the fountain solution of the press. PA1 (1) image-wise exposing to radiation or heat an imaging element comprising on a lithographic base at least one radiation sensitive or heat-sensitive layer composition, the composition being such that when exposed and developed, a lithographic surface is formed; and PA1 (2) developing the thus obtained image-wise exposed imaging element by contact with a single developing fluid, characterised in that the image-wise exposed imaging element is developed by passage along a plate path through a closed treatment cell in a processing apparatus containing the single developing fluid, wherein the closed treatment cell comprises a housing having an entrance and an exit each closed by a path-defining roller in contact with a reaction surface to form a nip therebetween, through which the plate path extends, and sealing means sealing each path-defining roller to the housing.
This known method suffers from the disadvantage that quality control of the printing plate is not easily possible. Debris from the development process, which accumulates in the liquid which serves both as the developing fluid and the plate wetting fluid, may potentially disturb printing quality. Furthermore, this construction has the disadvantage that the treatment liquid may become contaminated by the environment, especially by evaporation, oxidation and carbonisation thereof.